Characterization of Macrophage Activation Induced by Leukotoxin from Aggregatibacter actinomycetemcomitans 

Sammanfattning: ABSTRACT  Aggregatibacter actinomycetemcomitans (Aa), is a gram-negative, facultative anaerobe, non-motile coccobacilli colonizing the human oral cavity and is strongly associated with localized aggressive periodontitis (LAP). Aa possesses several virulence mechanisms, among others; Lipopolysaccharide (LPS), an endotoxin found in the outer membrane of Aa and Leukotoxin (LtxA), an exotoxin attached to the bacterial cell surface or in outer membrane vesicles and which has been correlating with periodontal disease mostly. LtxA specifically targets human leukocytes, causing imbalance in the host inflammatory response. It is involved in the activation of a cellular pathway, starting with ATP release from the cell, possibly through Pannexin-1(Panx-1) channels, Caspase-1 activation and release of bioactive interleukin-1β (IL-1β) from leukocytes. In the case of periodontitis, inflammatory cytokines like IL-1β will stimulate periodontal tissue breakdown. The aim of the present study was to examine the involvement of Panx-1 in LtxA induced activation and cytotoxicity of human macrophages.  To determine viability of the macrophages the release of LDH and the accumulation of neutral red was quantified. The release of IL-1β was analysed by ELISA analyses of the cell culture supernatants. Results showed that macrophages treated with Cbx and exposed to LtxA was still sensitive to LtxA, but showed a decrease in the IL-1β release. In opposite, macrophages exposed to LPS showed increased IL-1β release in presence of Cbx.  The conclusion of our study is that Panx-1 channels are partially involved in the cellular pathway leading to IL-1β release on LtxA exposed cells.